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In order to evaluate the expression and secretion signals of the highly secreted subtilisin inhibitor of Streptomyces venezuelae CBS762.70 (VSI) for the production of heterologous proteins by Streptomyces lividans, mouse tumor necrosis factor alpha (mTNF) was chosen as a model protein. The mTNF cDNA was fused to the vsi signal sequence. The analysis of secretion by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and biological activity measurements revealed an efficient translocation of mTNF. Up to 300 mg of secreted biologically active mTNF per liter could be obtained in shaken-flask cultures. By analyzing the effects of mutations in the N region of the VSI signal peptide on secretion, we found that decreasing the +3 charge of the wild-type protein to +2 resulted in a 3- to 10-fold increase in secretion.

Lactobacillus amylovorus LMG P-13139, isolated from corn steep liquor, produces two bactericidal peptides with respective estimated molecular masses of 4.5 and 6.0 kDa upon denaturing sodium dodecyl sulfatepolyacrylamide gel electrophoresis. The antimicrobial activity detected in the fermentation supernatant fraction of L. amylovorus LMG P-13139 was heat stable (20 min, 121 degrees C), displayed a narrow inhibitory spectrum, and was sensitive to proteinase K, trypsin, and alpha-chymotrypsin but insensitive to alpha-amylase, lysozyme, catalase, and lipase. The 4.5-kDa bacteriocin was purified and characterized and designated lactobin A. Lactobin A was isolated as a floating pellicle from culture supernatant brought to 35% saturation with ammonium sulfate. Upon this ammonium sulfate treatment, crude lactobin A was incorporated, together with Tween 80 as a major contaminant, in high-molecular-mass complexes sized at approximately 670 kDa by gel filtration chromatography. Contaminating fatty acids were removed from these micelles by a simple one-step methanol-chloroform extraction without loss of activity. Both inhibitory peptides were separated in an isocratic isopropanol gradient on a PepRPC 5/5 reversed-phase column, and both peptides retained activity towards Lactobacillus helveticus ATCC 15009 upon separation. Lactobin A has a molecular mass determined by electrospray mass spectrometry of 4,879 +/- 0.69 Da. Its peptide chain contains 50 unmodified amino acids, of which 26% are glycine residues and 40% are hydrophobic residues (A, V, L, I, and P). It displays the highest structural homology (42% identity and 28% similarity) with the lafX gene product, encoded by the second open reading frame of the lactacin F operon. These data strongly indicate that lactobin A belongs to the class IIb bacteriocins according to the classification of Klaenhammer.